Method of telegraphic communication



Dec. 8, 1942. .Y

H. J. J. M. DE REGNAULD DE |aE|.|.rasc|zr-:`

METHOD 0F TELEGRAPH I C COMMUN CAT ION Filed Aug. 11..1`9s9 s sheets-shet 1 1 laffe/:Z Mmm/LT A @me d I' I I L.I E x a Peo/e' m27 fig Eg'. Z

Dec. s, 1942. A 2,304,077

H. J. J. M. DE REGNAULD DE BELLESCIZE METHODv OF TELEGRAPHIC COMMUNICATION Filed Aug.' 11. 193s' 3 Sheets-Sheet 2 Y Dec. 8, 1942.

H. J. J. M. DE REGNAULD D-EIBELLESCIZE- METHOD OF TELEGRAPHIC COMMUNICATION 3 Sheets-Sheet 3 Filed Aug. 1.1. 1939 gli! | I l l YPatented Dec. 8, 1942 NlTED STATES fr ortica METHoD 0F TELEGRAPHIC COMMUNICATION Henri Jean Joseph Marie de Regnauld de Bellescize, Neuilly-sur-Seine, France; vested in the Alien Property Custodianv 12 Claims.

The dominant characteristic of radio communication is the enormous uctuation in the ratio of signal to interference; in a short wave link of average diiculty this ratio commonly varies byy 70 decibels in the course of a day, and occasionally by much more. A partial remedyfor this state of things is to increase the effective power of the transmitter on the one hand, and on the other hand continuously to adjust the characteristics of the traic so as to keep the percentage of errors sufficiently low; the adjustment consists in varying the speed of working and, when necessary, in repeating telegrams, which is the oldest and best form of the method of diversity. But

all these means do not alford a sufcient remedy;

when the field intensity of the signal is high and the Statics weak, the maximum speed of working permitted by the relays, or by the band width of the link, is well below that `which the momentarily favourable condition would in principle allowf to be attained; and on the other hand when the signal field is too weak and the interference too intense, it is better to stop traffic altogether than to slow it down excessively. Whence two important consequences:

(a) A rate of working, including repetitions, which is maintained within reasonable limits al-v lows during most of the time considerable traffic speeds while yet affording an unused and exces sive margin of safety, but at certain moments, happily brief and rare, becomes impracticable.

(b) The signals issuing from the radio receiver must be deciphered in order to supervise the pro" portion of errors and correspondingly adapt the radio-electric service to the constantly changing' state of the ether, and then must be re-coded to go by wire at the constant speed appropriate to the addressees printers; this double transforma; tion causes loss of time and substantial expense, the reading and re-transmission of telegrams calling for a numerous specialist personnel; it is besides a source of error, and impairs the secrecy of correspondence since it prevents users communicating directly with each other with apparatus and telegraphic codes of their own choice.

I-Iitherto it has not been found possible to reconcile a secret and economical terminal service with the optimum output that is obtainable only by constant adaptation to the varying state of the ether. This apparent incompatibility is one of the causes of the high cost of telegrams.

The present invention makes possible-an economical, and above all more certain, telegraph service, by re-organizing it with the aid of a comdr bination of improvements allflowing' from onef's` and the same initial achievement that is based on a principle already laid down iny my application Serial No. 160,330, filed August 21st, 1937, now Patent 2,176,168, 'issued October 1'7, 1939.

This fundamental achievement is a radio receiver whichcan produce only three effects, de-

pendent on permanent localconditions, suchY as'l ard form of the letter p, made up of a group of eleven dots and spaces all of the same duration T; in the middle of the figure is a distorted record of the letter; at the bottom is the result' obtained` in accordance with this invention; theeleven elementary signs are there assumed" toy have been identified andV re-constitutedy save 'the fourth which is replacedl by a dash of length T inscribed on a line of uncertainty :c distinct from the lines d and s appropriate tothe dots andspaces ofthe code respectively.

As this rst result governsl the other'objectsV of the invention, the principle on which it rests will at once be explained by the aid of 'Figures 2 and 3. It is assumed' that the Areceiver supplies tothe terminals O a rectified current which takes the values -l-I and -I in response to dots and spaces of the code received without any interference, and a value i varying at random between +I and -I when, on the contrary, the signal wave is dominated by static; these conditions are Vapproximately realised whenl a signal wave, frequency modulated toconvey the dots of the code by the frequency F-l-f and-thel spaces by the frequency F-f, is received in a filter having these frequencies as'the limits of its pass band, is then limited in amplitude, and finally is demodulated by any means which converts fluctuations of frequency into fluctuations of current intensity. A distributor l, analogous to that at 69,l Fig. 6, is synchronised with another at the radiating station to control the cadence of the signals; it closes the contact 2 for the duration of the sign in course of being received, then closes the contact 3 during a succeeding interval of time of substantially the sameduration T,

according as the signal has been Wholly free from interference or entirely dominated by interference; these are the limiting cases.

It may be seen from Figure 2 that V is lnecessarily much greater than o; and the probability of the ratio o/V being less than any given proper fraction K, i. e. of the condition o KV being satisfied, may be made as high as desired; ali that is needed is to increase the number of in,

dependent values assumed by the current intensity i in the course of an interval of time T,

that is to say to increase the ratio T/t between the duration of a code sign and the time constant or the filters with which the receiver is equipped; such increase results immediately from a lessening of the speed of Working, which factor plays an important part in the present invention as a means of adapting the service to the varying state of the ether; for example, if t=l/400 of a second (or the filter has a band Width 2f=400 c./s.) and T=%0 of a second, there isa 98 per cent chance that the voltage 'o nally developed by the most intense static Will be less in arithmetical value than 0.5 v., that is less than half the voltage V normally developed by a code sign received without interference. At the end of the sign the distributor closes the contact 3; the grid of the tube 5 is then brought for the duration of the next interval to the voltage so acquired by the condenser; relay 6 is adjusted so that it closes contact l if this voltage is less than, say, -0.5 v., and closes contact 8 if the voltage exceeds -}0 5 v. The grid of tube 9 then acquires the potential D or S for a code dot or space received Without interference, and 98 times out of a 100 the potential X if the sign just ended has been entirely covered by interference. The undulator I0, therefore, during the interval of time T during which contact 3 is closed marks a dash along one of the corresponding lines d, s or :c on the tape I I, these being the lines already shown in Figure 1. When interference is very intense there remain two chances in a hundred that the voltage of the condenser 4 Will have exceeded in arithmetical value 0.5 v. at the instant when the distributor opens the contact l, and of these one chance in a hundred is that the undulator by chance marks a dash of duration T reproducing the sign just ended, and the remaining one chance in a hundred is that the undulator reproduces the opposite sign which would be an error.

.In all, interference dominating the signal Wave throughout the duration of a sign will have 98 chances in a hundred of producing the mark of uncertainty and one chance in a hundred of causing an error; with an ordinary receiver it would have one chance in two of producing an error. Obviously this case of interference dominating the whole of the sign is the most unfavourable case; in telegraphy by frequency modulation interference of less intensity than the signal wave is practically innocuous, and does not much alter the voltage -}V or -V to which the condenser 4 should be brought at the end of every sign; so the undulator marks the proper dash on the line d or s. The same holds when the disturbing discharge dominates the code sign during only a part of its duration. The important fact to hold in mind is that only three possible events can occur during each closure of contact 3 with the condenser 4 retaining the charge acquired in response to the sign just ended: either this sign is reproduced in its normal form as if the disturbance had not existed, or during the same interval of time T there exists a current .r indicatuing uncertainty, or a real error is produced, cur- ',rent d being recorded instead of current s or viceof uncertainty zc, so that all accidents producek this same eiect. s.

This first object of the invention alone secures two advantages: The fact that most of the signs have recovered their standard forms enables automatic printers to be used, sensitive as they are to the least irregularity; moreover, error becomes almost impossible for the printer can be built to print a special mark in response to the effect a: which does not correspond to any code sign; it is then seen that such and such a letter is simply missing in the text, which is much preferable to the printing of a wrong letter at a point which naturally cannot be located. To these advantages are added two others: (a) a gain of about 9 decibels is obtained in the ratio of signal to interference, as much because the whole quantity of electricity delivered by each sign is accumulated as because the production of rectified currents in accordance with Figure 2 pre-supposes phase or frequency modulated signals which are less sensitive to interference than amplitude modulated signals, and (b) the printer becomes more certain than an undulator marking the fluctuations of the rectified current; for the interval during which contact 2 is closed by the distributor l constitutes in effect a preparatory stage which serves by the integration T fidi to analyse the general run of the rectified current during the sign; it is really a function identical with that performed by an operator carefullyy examining a record on a tape; but the operator is at a disadvantage for the double reason that the beginning and end of a much distorted sign can often not be discerned by sight, and that the time constants of usual receivers are at least four times less than the duration T of the analysis made bythe present process. The judg-` ment that this process renders upon each sign is asogow inafter described, necessitates modification of the construction of the distributor and the interposition of atube 5, the very high grid resistance of which permits the condenser il to retain the charge acquired.

The second object of the invention is to discover the percentage of signs impaired by static and fading without the need of deciphering telegrams as they come from the radio receiver; knowledge of this percentage makes it possible to adjust the speed of working to the Varying state of the ether. lf the code comprises only two signs, this information can be obtained by means of a relay adjusted to close a circuit during only those intervals of time T when the distributor i (Figure 3) feeds to the tube 5 a difference of potential less in arithmetical value than half the voltage (V) normally attained in response to one or other of the code signs; to that end it suflices, in principle,to shift the bias voltages D, S, making them sufficiently negative to cut olf the anode current of the tube 9, so that current ows only under the bias X. The time constants of the tube circuits can then be so designed as to average this anode current over a determined interval of time, and this average, which can be read upon a milliammeter, is a measure of the number of impaired signs during this interval. Any signal based on a Z-sign code would servev for thisI purpose; but as one of the aims of the invention is to organise a service'which will permit the public to use codes of its own choice, it is better to discover impairment by the aid of an auxiliary wave emitting dots and spaces alternately at a constant cadence. This wave will also facilitate neutralisation of frequency drifts and synspaces and dashes of the alphabet are transmitted by giving the signal wave the frequencies F-f, F, and F-i-f. The corresponding results in Figure 3 are then -V, O, and -l-V for the potentials fed to the grid of tube 5 when the distributor i closes contact 3, and s, :c and d for i the positions taken by the recording apparatus. As in ordinary receivers intense interference and fading now produce the same effect :r as one of the code signs; nevertheless the present process acquires or retains the two following advantages: the new code enables more words per minute to be transmitted on the sameband width, a speed of 100 bauds, i. e., 100 signs or spaces of T duration per second, delivering about 150 words per minute in Morse, about 200 in Baudot code, and about 300 with a three sign code; moreover the working of the printers is much more reliable thanks to the rarity of impaired signs and the perfect reconstitution of the rest. In fact, the degrees of safety obtained with codes of two and three signs respectively differ only in this, that in the former impairments appear as a mark of uncertainity, while in the latter they make an error. This difference may make two sign codes preferable for cipher It is proposed further to extend the use of,-

repetition. which permits correction of blanks or errors by comparison of two successive records of the same signal. Thiswell known method brings in the i time factor, Ithe advantage of which is to diversify both fading and interference; butit implies that disturbances affect only one of the two code signs, so that the other sign may be considered correct if it appears on one of. the records. Now this advantage is not fulfilled in ordinary' receivers, for their response to fading is the inverse of their response to static. By causing these two phenomenato producev the same effect, namely to mark a dash on` the reference line a' of Figures `1 and 3, the present invention removes ythis inconvenience; moreover acomparison of records becomes possibie whatever the number of signs in the code, since at most only one of these* signs normally marks dashes on the line :r also; recorded on the other lines in the course of one of the transmissions is necessarily correct. The

following advantage is thus attained; as each.

record comprises no more than three constituent elements, namely dashes of the same duration T inscribed on one of the lines d, s or these recor s can be brought into physical coincidence, or even be superposed upon a single tape; then, at any later time, everything recorded on the lines of this tape can be read automatically. For instance, it can be read by photo-electric cells, like those facsimile, connected in such fashion as to modulate the frequency of a telephone current actuating the addressees printer. This principle is illustrated in Figure 5, which shows two different distortedy records of the latter r, and below the result of superposing them; for the cells I2, I3 reading thelines d and s respectively, the record has become correct.

The two successive records can be made to coincide as follows; at the transmitter the perforated tape passes in succession through two Wheatstone transmitters W1, W2, one of which impresses on the carrier wave the frequencies Fiif and the other the frequencies Fzif; at the receiving station two receivers select these respective frequencies and actuate two undulators o1, o2, the tape taking as long to pass from o1 to ,o2 as the transmitting tape takes to pass from W1 to W2; these time intervals can be equalised once for all, since the speeds of travel of the tapes can be controlled by the synchronised distributors which control the cadence of the signs at the two stations; thus a sign already inscribed by the undulator o1 in response to the Wheatstone transmitter Wivcomes beneath the undulator o2 at the instant when it is repeated by the Wheatstone transmitter W2. ,The undulators must also mark uponA the same lines d, x, s, but that condition is easily fulfilled since it depends on simple abutments. stead of the undulators, perforators could be used adapted to re-act to the three intensities which the tube 9 of Figure 3 can provide. This method of automatic comparison of the records imposes no limiting condition upon them, and leaves theV parties communicating entirely free everything in use for the reading of Naturally, in-

' a telephone or other line is available.

The methods just explained all depend on the existence at the receiving station of a distributor synchronised withthat of the sending station. Now the analysis and reconstitution of the code signs on the principle illustrated in Figure 3, and the correction of blanks or errors by comparison of. successive records, are an improvement in transmission equivalent to a gain of many decibels in the ratio of signal to interference. This gain is conditioned by the synchronising of the distributors, but the synchronisation itself does not benefit from it; it must therefore have a wide margin of safety. It must also be made compatible with variation of the speed of working, by which the radio-electric service is adapted to the varying state of the ether. This two-fold condition would not be satisfied by occasional impulses, as used in the Baudot system in which of twenty-one consecutive signs only one is allotted to synchronisation. This consideration leads to the synchronising of the 4distributors by means of an auxiliary pilot wave, frequency modulated to transmit a succession of alternate dots and spaces of the same cadence as the code signs. Demodulation of this wave at the receiver gives an alternating current of period 2T upon which the motor driving the local distributor can be very rigidly locked. It is then possible to vary the speed of working at the transmitter by varying the speed of the distributor with which the Wheatstone transmitters are located; the synchronised apparatus at the receiver will follow these variations so long as they are sufficiently gradual. The pilot wave performing this function is that already serving to measure the percentage of signs impaired by fading and interference.

Recapitulating the above, the radio-electric service is made more reliable by the use of frequency modulated signals, by the utilisation of the whole of the current supplied by the detector, and most especially by a method which involves for each sign rst a more perfect analysis then examination of an undulator tape, and then a nearly infallible Vdecision the eiect of which is to reconstitute identifiable signs in their standard form and to make a special mark for signs which cannot be identified. This method makes the printer more reliable than the undulator; it replaces errors which cannot be located by easily located blanks, much fewer in number, and it permits automatic comparison of two successive records of the same signal to correct defects whatever be their cause; this comparison is a direct comparison of the currents fed from the receiver and imposes only one restriction upon the code, namely that it shall be analysable into signs of the same duration. Moreover, the radio service is accelerated both because interference causes less trouble and because new and faster codes can be employed. Communication between two correspondents no longer involves intermediate deciphering and re-coding; the percentage of defective signs is in effect given by an automatic indicator; the signs marked on the tape can be reconverted into currents which for the reasons already explained are adapted for the actuation of printers; the storage of tapes affords the time needed to wait for a line to become available and to allow for the difference of practice between the radio electric service. and the terminal service.

' traiic in clear on three sign codes.

The addresses of the addressee's alone (until auto-f matic directors are available) need be read at the' receiving station, but that does not detract froml the advantages due to direct utilisation of the records produced by the radio receiver.

Successive transmissions of a signal on two fre-I quency bands can be obtained, when circumstances call for it, by twinning two channels of a multiplex system. `Such a system is both economical, since buildings, land and antennae are common to all channels, and flexible since the channels can be employed at will either singly or two by two. For instance, two of them can be permanently associated to ensure maximum reliability in the transmission of cipher on two sign code, while the rest work sometimes singly and sometimes two by two to deal with Thus in one and the same station a scale of reliability is ob tained having steps enough to satisfy all requirements. A band width of 3,000 cycles makes seven channels possible, one for the pilot wave, and others for traffic; in three sign code the maximum output of this scheme exceeds 2,000 words per minute. Considering the degree of reliability already attained in telegraphy, in which interruption due to natural disturbances are rare, experiment proves that there is little gained by increasing the power radiated; the greater re-` liability which the present invention affords will therefore preferably lead to diminution of thek radiated power, and consequent reduction in the power of the machines, in the cumbrousness of aerials, and in the area of land occupied.

Figures l to 5 have served to illustrate the explanation above.

Figure 6 illustrates the construction of a telegraph system according to the present invention.

Figures 6a, 6b, 6c, 6d and 6e serve to explain various details of Figure 6, and

Figure 7 shows, in an alternative embodiment. the control of a magnetic recorder.

Figure 6 concerns the general organisation of a, multiplex telegraphy system between a local and a distant correspondent. The apparatus of the local service are illustrated in detail, while those similar to these, at the distant correspondent, are simply recalled by the same references followed by the index a. In one direction and the other, there may be any suitable number of channels; in the ligure, three channels have been indicated in each direction, viz. the rst reserved for the pilot wave, while the other two serve, separately or in combination, for the transmission of the communications. The local transmitting antenna I4 thus radiates three waves, the frequencies of which vary respectively between Fi-f and Fi-l-f, 3-f and Fs-I-f, F5-f and Fs-l-lJ while the local receiving antenna l5 receives those emitted by the distant correspondent on the bands Fzif, Fiif and Feif. The duration of all code signs transmitted by the local station and by its distant correspondent are denoted respectively by T1 and T2. The right hand side of the ligure concerns the local central telegraph station, where the traffic ,arriving by wire is transformed to modulate the transmitter, and that, received by the radio receiver undergoes the converse transformation for being transmitted by wire to the final addressee. The central part of the ligure represents above, the local radio transmitter, the partsv of which bear the references 22 t0 52 and I4,

. andbelow, those of the local radio receiver. The

`controls the relay 3d.

erated by users from a distance by the sending of proper currents. The perforated tapes pass either through the Wheatstone transmitter iii 'which when switch 2li is on Contact 2l controls the frequency of theFif channel by means of relays 22, 23, or in succession through the Wheatstone transmitters 24, 25, one of which, 2li, alnways controls the frequency of the F3 if channel by means of relays 2G, while the other,

25, may control the Fi- L-f channel when switch v is on contact 28. In the second case the same signal is transmitted first by transmitter 24 on the Fsif channel and then by transmitter 25 on the Fiif channel; the time interval between these transmissions is the ratio of the distance L- between the transmitters to the speed of travel of the tape E9; the distance L is a constant chosen yonce for all, say as equal to the length of tape occupied by one hundred code signs; the speed of travelof the tape is determined by the toothed Y.

wheel driven by the motor 3| which thus regulates the cadence of the code signs. This cadence .is made manifest at the receiving antenna 15a, oi the distant stationV by the emission of an uninterrupted succession of dots and spaces of vduration Ti, translated into the frequencies Fs-iand Fs-J of the pilot channel; for this purpose a distributor 33, also driven by the motor 3l, A rheostat serves for adjusting the speed of the motor and therefore the common cadence of the transmitters i9, 24, 25 and distributor 33; the use of a tangent screw 36 to adjust the rheostat necessitates the adjustment being made sufficiently gradually to be easily followed by the synchronised distributor at thedistant receiver. A key it? enables service messages to be sent through the channel Fii' if switch 2Q is put on contact 58.

tions from the roscillator '56.

Yra'diatedfby the antenna .M and .collectediby'the `receiinng lantennae 15a ofthe distant station.

'The waves radiated bythe transmitting Aantenna 14a of this distant Jstation are similarly collected by the local receiving antenna'l5, and after amplification in the 'HF amplifier 54 are reduced in frequency in the frequency changer in `which they are heterodyned with oscilla- The filters 51, 58, 5G seiect respectively the two signal waves Fai-f. and Fiif and the pilot wave Fsif which last is modulated by the distant station to the cadence of its code signs 0f duration T2. Consider v'first communication upon'the middle frequency F4; as Figure 6a shows, the band selected by the filter 5t is centred on Vthis Afrequency F4, and to allow for rthe speed of working its width is a little greater than the sum 2f of the Yfrequency variations into which the signs are translated. After selection, the signal vwave passes through a limiter Bil which stabilises its amplitude save'when fading is exceptional. The iiuctuations of frequency which now alone subsist are transformedinto fluctuations of a voltu; this can loe-done in `various ways,'for instance as described in my United States Patent No. 1,612,101 patented December 28, 1926; that method employs two resonators 6I, 62 tuned to the frequencies Fi-f and F4+f respectively, which supply detectors 63,164; allowingfor the filter 58 the output voltage u of this demodula'torv isa function of the frequency of 'the form shown Aby the line e of Figure 6b; lhencevit has The local radio transmitter comprises a master oscillator 39 of frequency Fo, which together with L generatorslii, 5:3 and 45 excites a modulator dii.

These generators are made of fairly low frequencies, and-their frequencies vary, in responsey to variation in the impedance of tubes d'2, M,

5, above and below mean values f1, f3, f5 which are separated by the desired intervals IPs-F3 and Fs-Fi between the three channels. The varia.- tions of impedance -o-f the tubes are brought about by relays which vary their grid bias; for instance the generator il has its mean frequency ,f1 when relay V22 applies the mean bias, and

its extreme frequencies i-f and ji+f according Aas the contacts of both relays are open, or the contact of relay 2331s closed; the amplitude f of the variations so obtained can be adjusted by simultaneous shifting of the tappings Iii', i8 one on each side cf the tapping which gives the mean bias. Cniy the relay 2.3 is in use to give the extreme frequencies required for a two sign code;

.the .relay 22 gives in addition the intermediate frequency needed for three sign codes. The frequency of the second channel is controlled in the saine way by relay 2l', and, if required, by relay 26. Since it only two frequencies, the pilot channel onlyT the relay Sii, the eifect of which can also be adjusted by shifting the bias tappings 49, 59. The 'Filter 5i sorts out one of the bands produced in the modulator it by the addi- .tion subtraction of the frequencies fiif, fazit-, and fs-i to and from the frequency F0. Oscillations in this band are amplified at 52,

the value -l-U for code dots translated into the "frequency Fi-l-f, the value -U for spaces, and

is zero orthe third code sign, if there be one, received on the mean frequency-F4. Fading too severe to be neutralised by the limitera'lso tends to bring'this voltage `to zero. As to oscillations due to statics, they are Lindiflerently any `frequencies passed bythe filter 58, so that in response to interference `u varies at Vrandom be- Vvtween the limits "-i-U and -U 'these are the conditions already illustrated by Figure 2 in connection with the theoretical vexplanation of the invention.

The variations of voltage u are transmitted to amplifying tube 65, preferably'placed at the `central Ytelegraph station; and theoutput current i of this amplier takes the values -l-I and '-I in response 'to the frequencies F4-i-f and Fai-j. Each ofthe condensers 66, 6'! in turn receives the quantity of electricity represented by this current flowing for the duration of a code sign,

and then in the next succeeding interval of time y T2 applies to the grid of the tube 68 4the potential v resulting from this charge; thus the condenser S6 deals with every other sign,and the condenser 61 with the intervening signs. They are caused so to operate by the distributors 69, 10, the brushes "H, l2 of which are displaced in relative phase by and are driven by the synchronous motor 13 at the rate of half a revolution per time T2. Figure 6 shows them in the position they occupy at the beginning of a code sign which is going to be recorded by the condenser 66. At this initial instant, the

condenser is short-circuited by the small sector le, and so is brought to neutral condition. Soon after the beginning of the sign the brush contacts with the sector 15 and remains in Contact with it nearly to the end of the sign; during this time the condenser receives the quantity of electricity supplied by the current z', and stores practically 'the' whole of it since the time constant of the circuit 66, 16 is made substantially greater than T2; the sector 15 is made to extend over a little less than a half circle to allow for possible slight errors in the setting of the synchronous motor 13. So the brush leaves the sector 15 a little before the end of the sign and at once contacts with the sector 11; the grid of tube 68'is then biased to the voltage v acquired by the condenser, and this voltage remains constant since the condenser is practically on open circuit, and the bias is maintained during an interval T2 because the sector 11 extends over a semi-circle. When the brush leaves this sector the recording of the sign is finished and the brush 12 then contacts with the sector 18 of the other distributor so as to apply to the grid of the tube 68 the voltage acquired by the condenser 61, thus recording is perfectly continuous; the resistances 19, 80 prevent the condensers appreciably discharging the one into the other should the sectors 11, 18 be in circuit together for an instant. It has already been shown that the voltage v normally reaches the values +V or -V in response to code signs translated into the frequencies F4+f and F4-f, and has a value almost certainly less than 0.5 v. when Statics dominate a sign from its beginning to its end. Relays 8|, 82 are therefore set the one to close contact 83 for voltages less than 0.5 v. the other to close contact 84 for voltages greater than 0.5 V.; such setting is illustrated by Figure 6c where the position of the contacts is plotted on a scale of potentials. So as long as the sector 11 or 18 is in circuit one or other of the three following effects is obtained; either a code sign just received without notable interference on frequency F4-f brings about the closing of contact 83, the 'biasing of the grid of tube 85 to the potential 86, the excitation of relay 81 and the attraction of its armature 88 to extreme position, so that the siphon 89 of the undulator marks a dash of exactly duration T2 on the reference line s; or a code sign received on frequency F4+f brings about the closing of contact 84, the biasing of the grid of tube 90 to the potential 86, the attraction of its armature 92 by relay 9| and the shifting of the undulator to the line d; or, finally, a sign, either much distorted by Statics or fading or represented by the mean 'frequency F4 brings about the opening of both `contacts 83, 84 and the biasing of both tubes 8-5, 90 to the muchA more negative potential 93, with the result that neither of the relays 81, 9| is excited, and the Siphon, withdrawn by its spring 94, comes to rest upon its abutment 95 and marks a dash of duration T2 on the line of uncertainty x. These lines s, d, a: are perfectly definite; instead of actuating an undulator the relays 81, 9| could obviously cause blows upon a ribbon like a typewriter ribbon.

After selection by the filter 51 the signals of 1 the Fzif channel are demodulated and recorded in the same way, either on the undulator 96 if they are independent signals, or on the undulator 91 if they are a repetition of the signs already transmitted on the F4if channel. For the purpose of such repetition the distant station has Itwo Wheatstone transmitters like those 24, 25

in the local central telegraph station. Since they are both composed of dashes of duration T2 inscribed on the lines d, s or sc, the successive records are superposed, subject to accidental defect, provided the tape 98 takes as long to pass from the undulator 89 to the undulator 91 as the transmitting tape takes to pass from one Wheatstone transmitter to the other; once established, vthe identity of these time intervals is maintained indefinitely since the driving member 99 of the receiving tape is connected with the motor 13 which itself is synchronized with the motor driving the transmitting tape. Figure 5 showed an example of the result obtained by superposing the two successive records.

Insofar as connections can be established with the addressees by the lines I6, the tapes are automatically read either by facsimile apparatus if recorded by an undulator or by Wheatstone transmitters if the relays such as 81, 9| have been used to perforate the tape along the lines s, d, .'r. The figure illustrates the first arrangement; two photo-electric cells |00, |0| translate the dashes inscribed on the lines d and s into currents which, after amplification at |02 and |03, actuate the relays |04, |05 respectively. The excitation of relay |04 applies to the grid of tube |06 a voltage of audio frequency derived from the generator |01, and the resulting anode current of the same frequency is transmitted by transformer |08 to the line; the excitation of relay |05 similarly transmits a current of another frequency determined by the generator |09; the dashes inscribed along the line :1: are translated into interruptions of the current. Thus the addressees printer receives three indications, two representing code signs and the third representing either uncertainty or a supplementary code sign.

The pilot wave, the frequency of which is periodically varied by the distant station from Fs-f to Fe-f-f to mark the cadence of his code signs can serve in the local station to synchronize the motor 13 with this cadence, to control amplification, to neutralise the frequency drifts, and automatically to indicate thepercentage of imperfections due to interference or fading. After selection by the lter 59, the selected band of which is illustrated by g in Figure 6d, this pilot wave first controls the HF amplification by means of the rectifier I0 and the lead there is nothing special about this control; it should however, be slow enough not to follow selective fading which does not affect the several channels at the same instant. The wave is then stabilised in amplitude by the limiter I 2, then demodulated by.

means analogous to those already described but adjusted in a slightly different way; its resonators ||3, 4 are tuned, not to the frequencies of modulation, but to two frequencies F and F just outside the bounds of the filter 59; the output potential difference u' of the demodulator then varies almost linearly from one boundary to the other, as seen in Figure 6e; its values -U1 and +U2 obtained in response to the frequencies Fs-f and Fs-l-f cease to be equal and opposite if there is any frequency drift, and their mean is no longer zero. This property makes it possible to neutralise drifting of the heterodyne oscillator 5S; the mean of the voltage u obtained by means of the high time constant circuit ||6, ||1 is applied to the grid of the tube |I5; when this mean value ceases to be zero, the armature of relay ||8 closes one of the contacts 9 or |20, so modifying the charge of the condenser |2|, the bias on the grid of the tube |22, and therefore the anode impedance of that tube; if the connections are made in the right sense this variation of impedance corrects the frequency of the oscillator '5B until the mean of the voltage u becomes zero again and the armature of the relay resumes its position mid-way between the conthe distant station.

safeoacw tacts; the condenser |2I then keepslthe'charge it rent of period 2T2, since the antenna Matrans- `mits alternately dots and spaces .of duration T on the frequencies Fe-l-f and Fe-f respectively; it would be possible to amplify this current and :control by it a synchronous motor' driving the distributors such as 69, 10, the arrangement shown in the figure has the advantage of obviating all slip; the motor I3 drives a generator |25 which supplies alternating current that has also the period `2I'2 when the speed of the distributors is correct; 'the currents delivered by this generator and by the tube |23 interfere inthe detector tube |20, with the known result o'f producing in the anode circuit of that 'tube an interference current the intensity of which depends on the diierence in Vphase between the two alternating currents; the relay |21 is adjusted so that its armature is `balanced between the contacts |28, |29 fora difference of phase of, say, 90"; any departure from this value closes one of the contacts, and, through themedium of the amplifying tube |30, modifies the excitation `of the motor and therefore its speed; the rate at which such corrections are brought about is made greater than the rate at which the distant station can adjust the cadence of its signs by adjustment of a rheostat like the rheostat 35, 35

vshown at the local central station.

The automatic counting of impairments due to fading and staticsis YeiTected-bythe aid of tube |3|, the grid of which may be connected bya vswitch |32 either to the distributors |33, |34 of the pilot channel, or to the distributors IBS, .l0 of one of the signal channels; the latter must, however, in this case employ a two lsign code, so that the voltage 4v applied to the'grid of the tube |3| normally takes only two values +V and V. Differing from the scheme of relays 8|, 82,

here it is the simultaneous closing of the con-v tacts |35, |36 4of which use is made, this Aoccur- .ring when the voltage o falls by chance between the `values 0.5 v. and +05 v. Each closing of the contacts, caused by the distributors to last a uniform time T2, tends to bring the bias of tube vdischarge of the condenser through thehigh resistance |52 permits, for in normal conditions one or other of the contacts |35 or |35 is open nearly all the time. Thus the grid bias nally acquired by the tube |31 at any given instant is nearly proportional to a ratio the denominator of which is the time constant of the circuit |40, |42, and the numerator the total duration NT2 `or the N successive impairments that have occurred during an interval equal to this time ill -sign of a three sign code.

constant.` Nis the sole'unknown in this ratio;

the milliammeter M3 which measures the grid bias of tube "|31 may therefore'be graduated by calculation to indicate directly the number N of impairments which .have occurred in a given lapse of time, say 20 seconds. This information enables the supervisor of the local service to give the distant transmitter directionslas to the speed of working, and if necessary for the repetition of signals. Such orders are transmitted by the key 137 shown beside the indicator |43.

In the sameway, the local service receives from the distant station orders concerning the adjustment of the rheostat 35 which controls'the cadence of the signs, and of the switch 2t by which repetition is set .in train 'when required. Such orders come, for example, through the Fzif channel, .and are translated into variations of potential applied to the grid of the tube EM; in response to these variationsthe relay M5 applies to the grid of tube ii a more or lessnega tive bias which cuts oli or re-establishes the anode current of that tube. This current, made audible by the audio generator ld'l, actuates the loud speaker |43 shown beside the rheostat 36.

Various detail modications may of course be performedzin the device of Figure 6 without departing from the frame of the invention.

For instance, the -marks made on the reference .lines d, s, .r by the currents issued from the receiver could be traced on rolls of sensitive paper similar to those used in fac-simile receivers.

According to another 4alternative embodiment,

illustrated in Figure '7, the three efiects which' may be set up bythe receiverare materialised'no longer visually on three lines, but magnetically by recording afrequency and/or amplitude modulation-on the lsteel wireof a magnetic recorder: The tube 68 and the relays 8l, 82 are those already represented in channel Fiif of Figure 6;

Athe closing of contact vB3, obtained when the voltage c delivered by the distributor to the grid of this tube is less than 0.5 v., subjects the grid Vof tube |49 to-a bias of musical frequency f supplied by the source |150; the closing of contact 8d, obtained when v 0z5 v.sets up a bias of a different frequency f supplied by the source |5l, while the simultaneous opening of contacts 83, 8d, obtained when v lies between 0.5 v. and -l-0-5 .v will carry the grid of tube Ult to the permarient bias 03, which may be sumciently negative for suppressing the anode current of this tube. The electromagnet |52 will therefore be subjected, at the end oi each sign, to one of the following three effects, which, by the-synchronous distributors, are imposed for the constant duration T2: a current 'of frequency f representing one of the 'code signs, a `current of frequency f" representing the second sign, and a constant or zero current expressing the state oi uncertainty and further capable ofrepresenting the third This frequency and amplitude modulation alters the magnetisation of the steel wire |53driven by the wheel 9% connected with the synchronised motor i3. As before, the signal may be repeatedover the channel Fzztf, in which case the terminal electro-r magnet of this channel, |54, will. confirm `the magnetic recordings already set up bv the electromagnet |52 or fill up the places which may vhave been left empty, represented by the regions of the Wire where the -magnetisation had `remained constant during the'irst transmission. At any Asubsequent moment, the magnetsation variations may be retransformed into .current variations capable of actuating the "printers, after which the wire is brought back to the neutral state in order to permit the recording of new signals.

In short, the process may `serve for materialis- `ing the received signals, in a manner to permit their correction by repetition, and then their storing until a line for transmitting them further has become free.

What I claim is:

l. A system for telegraphic communication by codes built up of grouped signs of unit length, which comprises, means for demodulating the received wave so as to transform this wave into a current of Varying intensity, means for substantially accumulating the electricity supplied by this current over each `unit length, means responsive to the result of this accumulation for producing at the end of this unit lengthv one of three definite effects, two of said effects normally representing two of the code signs While the third represents as indifferent condition of known significance, means for maintaining each of said produced effects over a following unit length, and means for utilizing this effect while it is thus maintained.

2. In radiotelegraphic communication liable to disturbances such as fading and static, and utilizing codes made up oftwo distinct signs of unit length, a receiver which comprises, means for demodulating the received wave so as to transform this wave into a current of varying intensity, means for substantially accumulating the electricity supplied by this current over each unit length, means responsive to the result of this accumulation for producing at the end of this unit length one of three denite effects, two of said effects normally representing the respective signs and the third representing either disturbed sign, means for maintaining each produced effect over a following unit length, and means for utilizing this effect while it is thus maintained.

3. In radiotelegraphic communication liable to disturbances such as fading and static, and utilizing codes made up of three distinct signs of unit length, a receiver which comprises, means for demodulating the received wave so as to transform this wave into a current of varying intensity, means for substantially accumulating the electricity supplied by this current over each unit length, means responsive to the result of this accumulation for producing at the end of this unit length one of three definite effects, two

of said effects normally representing two of said signs respectively and the third representing the third normal sign and any disturbed sign, means for maintaining each produced effect over a following unit length, and means for utilizing this effect while it is thus maintained.

4. A radio telegraphic system for codes based on the grouping of signs of equal duration comprising a transmitter radiating a signal wave modulated in response to these signs, a receiver, means responsive to the combined action of the transmitter and receiver to produce in the output of the receiver a current the intensity of which assumes two constant values in response to two of the code signs respectively and varies at random between these values in response to Statics and fading, a distributor synchronised with the cadence of the signs to accumulate while each sign lasts the quantity of electricity conveyed by said current and then to maintain and utilise during an interval of time equal to the duration of the sign the voltage due to such accumulation, voltage-controlled apparatus having two thresholds of response beyond the voltages which can be produced by the accumulation of variable current due to Statics, and means for obtaining from this apparatus three definite effects of the same duration, two of said effects being obtained when the voltage reaches one or other threshold of response respectively, While the third effect is obtained when neither threshold is reached.

5. In radio telegraphic communication by codes based on the grouping of signs of the same duration, individually represented by a particular frequency of the signal wave, a receiver including a selective filter selecting substantially the band upon which the communication is transmitted, a demodulator which transforms variations in frequency on one side and the other of the middle frequency of the filter into variations in intensity of current, so that in response to statics said current takes any intensity intermediate between those corresponding to the limit frequencies of said filter, two condensers, a vacuum tube with a control electrode, two distributors synchronised with the cadence of the code signs and associated with said condensers respectively so as each in turn to perform within the duration of two code signs three consecutive operations, the first of short duration being to short circuit the condenser to discharge it prior to the sign about to begin, the second operation occupying nearly the .whole duration of this sign and consisting in the accumulation in the condenser of the charge supplied by the current, the third operation occupying a time exactly equal to the duration of every sign and consisting in applying to the control electrode of said tube the voltage resulting from the charging of the condenser, a system of relays actuated by said tube and adjusted to close two contacts, one for the voltages a little below and the other for voltages a little above the eXtreme voltages which the condenser can acquire from the variable current due to Statics, and means for obtaining from said relay system one of three effects, two of them corresponding respectively to the close of one or the other of the contacts and the third to the simultaneous opening of both contacts.

6. In radio telegraph communication in which the receiver at the end of each sign can produce one of only three definite effects of the same duration, of which two normally represent two of the signs and the third represents an indifferent condition of known significance, the method of correcting errors due to Istatics and fading, which consists in feeding a message tape to a transmitter repeatedly for transmitting the same signal a plurality of times, in recording the successive effects obtained in response to each transmission, in making the records coincide for comparison, and in scanning the coincident records so as to translate them into their corre'- sponding intelligence by rejecting recordations of the third effect where a recordation of any one of the other effects is concurrent therewith.

7. In radiotelegraphic communication in which the receiver at the end of each sign can produce one of only three effects of the same duration, of which two normally represent two of the signs and the third represents an indifferent condition of known significance, the method of correcting errors due to statics and fading, which consists in feeding a message tape to a transmitter repeatedly for transmitting the same signal a plurality of times, in marking a record tape in three lines, corresponding respectively to said three eiects, in accordance with the effects obtained in response to each transmission, in making the records coincide for comparison, and in scanning the coincident records so as to translate them into their corresponding intelligence by rejecting recordations of the third effect where a recordation of any one of the other eects is concurrent therewith.

8. In radio telegraphic communication in which the receiver can only produce at the end of each code sign one of three eiects of the same duration, two of said effects normally designating two signs and the third designating an indifferent condition of known significance, the method of repetition for correction of errors which consists in feeding a message tape to a transmitter repeatedly for transmitting the same signal a plurality of times and at convenient intervals of time, in marking a record tape in three lines, corresponding respectively to said three effects, successively in accordance with the effects obtained in response to each transmission, and passing said tape from one recording position to a succeeding recording position in a time equal to the interval between the corresponding transmissions, so that the records are superposed on the tape save for distorted signs which are all recorded on the line corresponding to said third effect.

9. A system applicable to radio telegraphic communication for automatically discovering distortion due to disturbances such as fading and Statics, comprising means for producing in the receiver output a definite effect in response exclusively to such disturbances and means connected with the aforesaid means for summing such effects over a determined interval of time.

10. A system applicable to radio telegraphic communication for indicating automatically the seriousness of trouble due to disturbances such as statics and fading comprising means for producing in the output of the receiver a current of constant intensity and duration in response to each code sign distorted by disturbances eX- clusively, so that each distortion is represented bythe production of a definite quantity of electricity, a circuit includinga condenser and a resistance, said condenser being connected with said means and operative for accumulating the definite quantities of electricity produced during an interval of time equal to the time constant of said circuit made up of said condenser and said resistance, and means for indicating the voltage acquired by the condenser as the result of such accumulation as an index of the effects of Statics and fading.

11. In radio telegraphic communication by codes based on the grouping of signs of the same duration following each other in a definite cadence, apparatus for enabling variation of the cadence comprising at the transmitter means for generating an auxiliary wave, for modulating said wave at a frequency which is a function of the cadence of the signs, and for impressing at will upon the cadence gradual variations the rate oi which is limited, and comprising at the receiver means for converting the auxiliary wave into an alternating current of the frequency of modulation of the wave, local distributors operative at the cadence of said signs, a motor for driving the local distributors, and means for synchronising said motor with said current, said synchronising means having a time constant related to the limiting rate of Variation of the cadence at the transmitter.

12. In radiotelegraphic communication liable to disturbances, such as static and fading, and utilizing codes made up of grouped signs of unit length, a receiver which comprises means for demodulating the received wave so as to transform this wave into a current of varying intensity, means for substantially accumulating the electricity supplied by this current over each unit length, means responsive to the result ci this accumulation for producing at the end ci' this unit length one of three definite effects, two of said effects normally representing two of said signs respectively while the third represents an indifferent condition of known significanoe, and means for collecting the produced effect over a following unit length.

HENRI JEAN JOSEPH MARIE; mi

REGNAULD DE BEILESCIZE. 

